lol size 8.5 you wont have any problem. you can probably move the bindings back a little and center the boot more on the bindings.
its when people with size 12 riding less than 160cm boards having problem.
btw that top sheet is so beautiful. I like a wood grain pattern.

Nevertheless, did you do the angle test? Press the camber into the floor/table/counter and lean your board up on the toe edge until your toe or any part of the bindings start hitting, note the angle (even visual is fine for this).

Then do the same thing on the heel edge, until the boot or any part of the bindings hit. Note the angle.

Adjust until both those angles are relatively even. You don't have an overhang problem, just trying to help you centre the setup on the board.

For what it's worth, most boards I ride are right around the 25.0 cm mark and I have size 8 boots. I picked up a Nitro Slash 166 cheap this fall expecting it to handle like a boat, but it's a lot of fun! 26.4 cm waist width...

Maybe move the bindings a bit towards heelside if you want to have them more perfectly centered. But it looks fine as it is.

2mm at the waist mean nothing. And... did you really calculate it's 0.8% ??!! It's actually 0.79%.
That was a waste of time. Not only 2mm are nothing, but If the other board has a different sidecut then those 2mm will have no impact on the width under your feet.